Australia's Ariarne Titmus has reclaimed the women's 400 metres freestyle world record with a stunning victory at the world championships in Japan.

Titmus emphatically blew away feted rivals Summer McIntosh from Canada and American great Katie Ledecky to triumph in Sunday night's hyped final in Fukuoka.

The Australian clocked three minutes 55.38 seconds, bettering McIntosh's world mark of 3:56.08 set last March.

'I was really excited for this race [...] Katie and Summer always put up a great fight,' said Titmus, who held the benchmark time for 18 months before McIntosh's March feat.

'It's just great to be a part of it.'

Titmus finished 3.35 second ahead of Ledecky, with McIntosh in third place some 4.21 seconds behind the Australian.

Earlier, Australia's Sam Short put a golden stamp on his arrival as a swimming force, winning the men's 400m freestyle.

Short adds his name to a rich Australian history in the 400m freestyle featuring legends Ian Thorpe, Grant Hackett and Kieren Perkins.

'They're my heroes,' Short said.

'They are some of Australia's best athletes ever. It's an honour to be with them.

'And hopefully I can continue to move forward and one day rival Thorpey in the rankings.'

The 19-year-old Short, the youngest swimmer in Sunday night's final, pipped Olympic champion Ahmed Hafnaoui by 0.02 seconds.

Short led at every 100m mark before the Tunisian challenged in the last 50m.

'I knew he won that sprint finish in Tokyo - he's a big guy, I could see him coming at me that last 100," Short said.

'And that last 25, I threw everything at the wall.

'I am stoked. I couldn't wait to get on the lane rope and start flexing to be honest.

'It's what you dream about as a young guy.'

Short's winning time of 3:40.68 is the fourth-fastest ever and just 0.61 seconds outside of German great Paul Biedermann's world record set 14 years ago.